The present invention relates to a distance gauge and distance measuring method, and more particularly, to a method for measuring the center distance between holes with parallel axes, and a distance gauge which assists in these measurements.
Accurate measurement of the distance between parallel axes of machined holes is required, for example, when the holes are designed to house bearings which define the rotational centers of mating gears in a precision gearset. Prior-art methods vest accuracy either in a machine tool's integral measuring system, or in external devices such as vernier calipers and optical position indicators. In the integral system, axial separtion between holes is determined by measured movements along machine tool axes from one hole axis to the coordinate or polar site at which the location of the second feature is desired. Movement distances are governed by changes in readings of coordinate and angular dial settings of the machine. In the usage of external devices, the machine-tool settings are audited by readings taken from external position readouts, which readings reaffirm the center distance measurement.
The major problem encountered in generating two precision holes established between a precise interval has involved accurately centering a measuring instrument in a hole whose diameter changes with each pass of the boring tool. As the second hole's feature size (preferred diameter) is approached, more frequent confirmation of the holes location relative to its datum become necessary.
Prior-art distance gauges have been required to have hole center "finders" which must be precisely centered in the hole as well as being carefully tilted so as not to cause an error in measurement of the distance between the centers of the holes. The construction of conical measuring heads, as in U.S. Pat. No. 3,289,307, is one attempt to solve the problem, but the center of the probe must still be positioned precisely above the center of the hole, and this is difficult, as well as time-consuming.